Longitudinal monitoring of asthma in the clinic using respiratory oscillometry

Background and objective Asthma guidelines emphasize the importance of assessing lung function and symptoms. The forced oscillation technique (FOT) and its longitudinal relationship with spirometry and symptoms are unresolved. We examined concordance between longitudinal spirometry, FOT and symptom control, and determined FOT limits of agreement in stable asthma. Methods Over a 3‐year period, adults with asthma attending a tertiary clinic completed the asthma control test (ACT), fraction of exhaled nitric oxide (FeNO), FOT and spirometry. Analysis included between‐visit concordance for significant change using Cohen's kappa (κ) and stable asthma FOT limits of agreement. Results Data (n = 186) from 855 visits (mean ± SD 4.6 ± 3.0 visits), 114 ± 95 days apart, were analysed. Between‐visit concordance was moderate between reactance at 5 Hz (X5) and forced expiratory volume in 1 s (FEV1) (κ = 0.34, p = 0.001), and weak between ACT and FEV1 (κ = 0.18, p = 0.001). Change in FeNO did not correlate with lung function or ACT (κ 0.1). Stable asthma between visits (n = 75; 132 visits) had reduced lung function variability, but comparable concordance to the entire cohort. Limits of agreement for FEV1 (0.42 L), resistance at 5 Hz (2.06 cm H2O s L−1) and X5 (2.75 cm H2O s L−1) in stable asthma were at least twofold greater than published values in health. Conclusion In adults with asthma, there is moderate concordance between longitudinal change in FOT and spirometry. Both tests relate poorly to changes in asthma control, highlighting the need for multi‐modal assessment in asthma rather than symptoms alone. The derivation of longitudinal FOT limits of agreement will assist in its clinical interpretation. We present longitudinal concordance of forced oscillation technique (FOT), spirometry and fraction of exhaled nitric oxide in asthma, and their relationship with symptom control. While concordance between FOT and spirometry was moderate, the weak association with symptom control highlights importance of multi‐modal physiological monitoring in asthma. Presented limits of agreement during stability provide a clinical interpretation reference. See related Editorial